The present invention relates to a radiation image erase unit for use with a stimulable phosphor sheet, and more particularly to a radiation image erase unit in the system in which a stimulable phosphor sheet with a radiation image stored therein is exposed to stimulating rays, and light is emitted from the stimulable phosphor sheet in proportion to the stored radiation energy and read out by an optical image read-out device for conversion into electric signals representing the radiation image. The radiation image erase unit is arranged such that when the radiation image which remains on the stimulable phosphor sheet after the irradiation image has been read out is to be erased upon exposure to erasure light, the heat radiation from the erasure light source is forcibly discharged out to protect the stimulable phosphor sheet from adverse effects of the heat thereon.
There has in recent years been proposed an radiation image recording and reproducing system in which a radiation image of an object can be produced by using a stimulable phosphor. The stimulable phosphor, when exposed to a radiation such as X-rays, .alpha.-rays, .beta.-rays, .gamma.-rays, cathode rays, or ultraviolet rays, stores a part of the energy of the radiation. When the stimulable phosphor exposed to the radiation is exposed to stimulating rays such as visible light, the stimulable phosphor emits light in proportion to the stored energy of the radiation. The radiation image recording and reporducing system employs such a stimulable phosphor. More specifically, the radiation image of an object such as a human body is stored in a sheet having a stimulable phosphor (hereinafter referred to as a "stimulable phosphor sheet" or a "phosphor sheet"), and then the stimulable phosphor sheet is scanned with stimulating rays such as a laser beam to cause the stimulable phosphor sheet to emit light representative of the radiation image. The emitted light is photoelectrically detected and converted to an electric image signal which is processed to reproduce a visible image on a recording medium such as a photographic light-sensitive material or on a display unit such as a cathode ray tube (CRT). The aforesaid radiation image recording and reproducing system is disclosed in Japanese Laid-Open patent publication No. 55-12429 or 56-11395, for example.
The radiation image recording and reproducing system of the type described above is of greater practical advantage than conventional radiographic systems using a combination of an intensifying screen and an X-ray film in that images can be recorded in a wide range of radiation exposure. More specifically, it is known that the amount of light emitted from a stimulable phosphor upon stimulation thereof is proportional in a highly wide range to the amount of radiation to which the stimulable phosphor has been exposed. Therefore, even if the amount of radiation to which the stimulable phosphor is exposed varies widely under various conditions, radiation images free from such exposure variations can be obtained by selecting a suitable read-out gain in the photoelectric transducer for reading and converting the emitted light into an electric signal, and processing the electric signal into a visible image on a recording medium such as photographic light-sensitive material or on a display unit such as a CRT.
The radiation image recording and reproducing system is capable of processing a converted electric signal to produce a visible image on a recording medium or a display unit so that the radiation image can well be observed for diagnostic purpose. In this system, the stimulable phosphor sheet does not serve as a final image recording medium, but as a temporary image storage medium for eventually transferring images to the final recording medium or display unit. Therefore, the stimulable phosphor sheet can be used repeatedly, and is economical and convenient if in repetitive use.
To reuse the stimulable phosphor sheet, the residual radiation energy on the stimulable phosphor sheet after the radiation image has been read out by stimulating rays is discharged by exposure to light having a wavelength within the stimulating wavelength for the stimulable phosphor constituting the stimulable phosphor sheet. The erasure of the irradiation energy from the stimulable phosphor sheet is disclosed in Japanese Laid-Open patent publication No. 56-11392 or 56-12599, for example.
More specifically, it is necessary to discharge all of the radiation energy remaining on the stimulable phosphor sheet in order to erase any residual irradiation image. Therefore, the residual image should be completely erased by being exposed to as much intensive light emitted from an erasure light source as possible because if any radiation image remained on the phosphor sheet, it would adversely affect a next radiation image of the object to be stored on the phosphor sheet, and no accurate image would be available of the object.
In order to erase the residual image completely and in short time from the phosphor sheet with the erasure light, an increased number of erasure light sources and an increased amount of erasure light should be employed to generate intensive erasure light. The increased number of erasure light sources and the increased amount of erasure light however tend to heat the image erasure unit excessively. The image erasure unit, the stimulable phosphor sheet, and surrounding components are therefore liable to be damaged by the heat of the erasure light emitted. In addition, the generation of the intensive erasure light requires a large-size power supply which makes the entire system large in size and which also makes it difficult to maintain and service the system.
If the image erasure unit is to be more compact and installed in a smaller space, the number of light sources for emitting erasure light will be restricted and the amount of erasure light emitted will be reduced. Therefore, the stimulable phosphor sheet carrying a residual image to be erased should remain placed in the image erasure unit for an increased period of time. As a result, the cyclic period in which to use the stimulable phosphor sheet for the storage of a radiation image will be increased.